Hybrid Drive Transmission Unit and Method for Operating a Vehicle with a Hybrid Drive

ABSTRACT

A hybrid drive transmission unit for a vehicle with an internal combustion engine and an electric motor for the drive part, includes a power-split transmission with sub-transmissions and a torsion-damping unit with a gyrating mass interconnected between the internal combustion engine and the power-split transmission. A clutch is interconnected between the internal combustion engine and the torsion-damping unit, by which the internal combustion engine can be activated, switching from the electromotive operating mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/EP2018/069203, filed Jul. 16, 2018, which claims priority under 35U.S.C. § 119 from German Patent Application No. 10 2017 214 396.7, filedAug. 18, 2017, the entire disclosures of which are herein expresslyincorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a hybrid drive transmission unit for a vehiclewhich, for drive purposes, has an internal combustion engine and anelectric motor, and also to a method for operating a vehicle with ahybrid drive.

Hybrid drives for vehicles, including motor vehicles, heavy goodsvehicles, rail-bound vehicles, ships and the like, are becomingincreasingly important in order to reduce the emission of pollutants andthe emission of CO₂. There are systems in which the internal combustionengine and the electric motor drive different axles, and there aresystems in which they drive the same axles or, generally speaking,output shafts. The invention relates to a hybrid drive transmission unitand also to a method for operating a vehicle with a hybrid drive, inwhich the internal combustion engine and the electric motor can drivethe same output shaft. In this respect, there are driving states inwhich only the electric motor, only the internal combustion engine orboth said electric motor and said internal combustion engine drive theoutput shaft.

The internal combustion engine usually has its own starter generator,that is to say an electric motor which requires a very large amount ofenergy for the purpose of starting the internal combustion engine. Thisenergy has to be permanently provided when the vehicle is driving in theelectric operating mode. This considerably reduces the power availablefor electric driving since the electrical power for the purpose ofstarting the internal combustion engine has to be permanently providedin the on-board electrical system and in the energy store.

Furthermore, consideration has been given to using the electric motorfor driving the vehicle for the purpose of starting the internalcombustion engine as well, but these systems require furtherimprovement. In particular, starting the internal combustion engineresults in an abrupt drop in power at the output shaft and undesired“jerking” of the vehicle.

The object of the invention is to provide an improved hybrid drivetransmission unit for a vehicle, in which the above disadvantages areavoided, and also to specify a method for operating a vehicle with ahybrid drive which likewise avoids the above disadvantages.

The object of the invention is achieved firstly by a hybrid drivetransmission unit for a vehicle which, for drive purposes, has aninternal combustion engine and an electric motor, comprising apower-split transmission which is interconnected between the internalcombustion engine and an output shaft and has component transmissionsand associated component transmission clutches, wherein the electricmotor is coupled to a component transmission which is close to theelectric motor in order to be able to drive the output shaft by means ofsaid component transmission. A torsion damping unit with an oscillatingmass is interconnected between the internal combustion engine and thepower-split transmission. Furthermore, a clutch is interconnectedbetween the internal combustion engine and the torsion damping unit. Theterms “which is close to the electric motor” and “which is remote fromthe electric motor” below do not relate to the spatial proximity butrather to the torque coupling which takes place directly into thecomponent transmission which is close to the electric motor.

The power-split transmission can be, for example, a planetarytransmission or a dual-clutch transmission.

The additional clutch is preferably seated firstly on the crankshaft andsecondly on the torsion damping unit, wherein the torsion damping unitis then additionally directly coupled to the input of the dual-clutchtransmission (here, the term “input” is related to the force flow duringdriving by the internal combustion engine).

Owing to the torsion damping unit with the oscillating mass which iseither separate or is integrated into the torsion damping unit, theelectric motor drives the oscillating mass in the electric motor drivingmode, kinetic energy then being stored in said oscillating mass. Thiskinetic energy and possibly yet further kinetic energy is then suddenlyintroduced into the internal combustion engine by closing the additionalclutch in order to bring said internal combustion engine to asufficiently high rotation speed, at which it is self-sustaining.Therefore, a higher electrical power is available for the startingprocess. Furthermore, it is possible to disable or to considerablyreduce an abrupt drop in the torque at the output shaft during thestarting process by appropriately intelligent shifting of the componenttransmission clutches. The interconnected clutch allows an abrupt pulsestart of the internal combustion engine.

The torsion damping unit is formed, for example, by a dual-massflywheel, a torsion damper or a so-called rotation speed-adaptiveabsorber. In this case, as already explained, the oscillating mass canbe part of the torsion damping unit, can be situated outside saidtorsion damping unit or an additional oscillating mass to an oscillatingmass which is already integrated in the torsion damping unit can beprovided.

The electric motor can be coupled to one of the two componenttransmissions, but in particular to that component transmission whichcontains 2nd gear, i.e. the 2nd lowest gear. This component transmissionis usually that of the so-called “even” gears, i.e. gears 2, 4, 6 etc.and possibly the reverse gear.

The electric motor should even be coupled fixedly in terms of torque toits associated component transmission, e.g. on the drive side of thecomponent transmission, between gear (i.e. the gear sets) and theassociated component transmission clutch.

The interconnected clutch between the internal combustion engine and thetorsion damping unit can be a rapidly shifting clutch which can beclosed in fewer than 150 msec, in particular 50 msec. It is alsoreferred to as a so-called digital clutch. Owing to this abrupt couplingof the crankshaft to the oscillating mass, hardly any heat is produced,and therefore the energy can be transmitted to the crankshaft with fewerlosses. The oscillating mass carries along the internal combustionengine as it were.

A sufficiently high rotation speed at the oscillating mass is criticalfor starting the internal combustion engine. This sufficiently highrotation speed can be generated in the driving mode by intelligentshifting of the two component transmission clutches. This is assisted byappropriate coupling of the electric motor by means of a suitableshifting strategy.

According to one variant of the invention, a corresponding controller,as part of the hybrid drive transmission unit, makes provision, afterstarting of the internal combustion engine is requested, for theoscillating mass, as soon as it has sufficiently high kinetic energy, tobe disconnected from the drive shaft, generally speaking from the outputdrive, by opening the component transmission clutches, so that theoscillating mass can rotate freely and the electric motor can provideall of the power for driving the vehicle. At least one of the twocomponent transmission clutches can be shifted over to the slip mode.Owing to the slip, the output drive is not completely disconnected fromthe internal combustion engine.

Therefore, a pulse start without a reduction in the electromotive poweravailable at the output shaft is subsequently possible. The hybrid drivetransmission unit according to the invention is particularly suitable inorder to start the internal combustion engine during start-up or in theso-called creep mode, for example up to 10 km/h, in particular up to 5km/h. At these low speeds, there are also only very low revolutionspeeds in the drive system, for example only approximately 300 rpm.These are usually not sufficient in order to start the motor by means ofthe crankshaft which is correspondingly brought to 300 rpm. Accordingly,the rotation speed has to be higher. This increase in the rotation speedwithout simultaneous acceleration of the vehicle takes place bycorresponding shifting strategies for the component transmissionclutches, wherein the controller is preferably designed such that theoutput-side component transmission clutch of the two componenttransmission clutches is shifted over to the slip mode. The componenttransmission or the component transmission clutch is on the output sidewhen it is the last component transmission or the last componenttransmission clutch in the force flow path to the output shaft.

After warm-up of the internal combustion engine, the slipping componenttransmission clutch can then be closed, and the torque of the internalcombustion engine is used for driving the vehicle.

The abovementioned object is also achieved by a method for operating avehicle with a hybrid drive and a hybrid drive transmission unit, whichis connected to the internal combustion engine and its crankshaft,according to the present invention, and also with an electric motorwhich is coupled to a component transmission, wherein a componenttransmission clutch of the component transmission to which the electricmotor is coupled is referred to as the “component transmission clutchwhich is close to the electric motor” in the text which follows. Thecomponent transmission clutch of the component transmission to which theelectric motor is not coupled is referred to as the “componenttransmission clutch which is remote from the electric motor” in the textwhich follows. The method according to the invention is characterized bythe following steps:

a) during the electric driving mode, the interconnected clutch is openedand the internal combustion engine is switched off, and

-   -   b) starting of the internal combustion engine by closing the        interconnected clutch and by transmitting the kinetic energy of        the oscillating mass which is driven during the electric driving        mode to the crankshaft in order to bring the internal combustion        engine to a self-sustaining rotation speed.

The interconnected clutch allows only the oscillating mass to be broughtto rotation speed, without the internal combustion engine having to becarried along.

Before closing of the interconnected clutch, the component transmissionclutches, for starting purposes in accordance with step b) and when aprespecified minimum rotation speed of the oscillating mass is reached,are opened or held in the slip mode, in particular wherein the electricmotor then furthermore drives the vehicle, on account of the permanentcoupling to one of the two component transmissions, until the internalcombustion engine applies a prespecified torque and takes over drivingof the vehicle. In this case, the energy which in the torsion dampingunit together with the oscillating mass in the moving parts which areseated between the component transmissions and the torsion damping unithas to be so high (i.e. the oscillating mass is at a prespecifiedminimum rotation speed) that the internal combustion engine can bebrought to the self-sustaining rotation speed with the aid of saidenergy.

If the internal combustion engine is to be started only upon start-up orin the creep mode, that is to say before a prespecified speed (inparticular approximately 10 km/h, further particularly 5 km/h) isreached when the vehicle is in the electric mode, the output-sidecomponent transmission clutch of the two component transmission clutchesis shifted to the slip mode before closing of the interconnected clutchand/or after closing of the interconnected clutch. The output-sidecomponent transmission clutch is that of the two component transmissionclutches which is the last of the two component transmission clutchestoward the output shaft in the torque direction. This has the followingadvantages: the electric motor can be ramped up without the vehiclebeing accelerated in the process. The increased torque then drives theoscillating mass and accelerates it further than would otherwise bepossible in the start-up mode or in the creep mode. When the output-sidecomponent transmission clutch is in the slip mode before closing of theinterconnected clutch, the jerking which occurs during starting of theinternal combustion engine can furthermore not be transmitted to theoutput drive. Instead, the output-side component transmission clutchcorrespondingly slips.

The output-side component transmission clutch, in the slip mode, isadjusted and the electric motor is brought to a rotation speed such thata required torque is applied to the output side by the electric motorand/or the oscillating mass is accelerated to the prespecified minimumrotation speed. This means that regulation takes place to the effectthat neither an abrupt jump in torque upward or downward takes place atthe output shaft for starting the internal combustion engine. Theinternal combustion engine is started in a manner which is imperceptibleto the vehicle occupants.

Immediately before the beginning of the slip mode, usually as early asduring the fully electric driving mode, the interconnected clutch isopened, so that the rapidly shifting clutch is indirectly decoupled fromthe output shaft by means of the slip mode. In addition or as analternative, the slip mode is maintained during starting of the internalcombustion engine in step b) in order to further assist starting andfurthermore to conduct torque to the output drive.

For starting in accordance with step b) at a low vehicle speed until aprespecified speed (creep mode) is reached and/or during start-up of thevehicle, the component transmission clutch which is close to theelectric motor is closed and the component transmission clutch which isremote from the electric motor is brought to a slip mode. This meansthat the total torque of the electric motor is available via the closedcomponent transmission clutch which is close to the electric motor,which total torque is split firstly for the purpose of driving theoscillating mass and secondly for the purpose of driving the drive shaftvia the component transmission clutch which is remote from the electricmotor.

In particular, provision is made, after closing of the interconnectedclutch, for the component transmission clutch which is close to theelectric motor to still be closed and the component transmission clutchwhich is remote from the electric motor to be in the slip mode. Thismeans that the electric motor assists, via the closed clutch which isclose to the electric motor and via the closed intermediate clutch, thestarting process of the internal combustion engine and provides, inaddition to the kinetic energy of the oscillating mass, additionalkinetic energy and torque.

After starting of the internal combustion engine in accordance with stepb), the component transmission clutch which is remote from the motor isclosed, so that the torque of the internal combustion engine can bepassed to the drive train without slip. When the torque which isintroduced into the power-split transmission by the internal combustionengine reaches or exceeds the torque which is introduced by the electricmotor, the component transmission clutch which is close to the electricmotor is opened, so that torque passes to the output shaft exclusivelyby means of the internal combustion engine. The electric motor is thenswitched off. This also ensures jerk-free transition between theelectric motor driving mode and the internal combustion engine drivingmode.

There are start-up situations or situations in which the vehicle is notdriven in the lowest gear, for example when starting to drive downhillor when the electric motor provides an enormous amount of torque. Inthese cases, the vehicle can start-up, for example, in 2nd or 3rd gear.However, this would then lead to the oscillating mass being brought toan excessively low rotation speed. The invention avoids this by way offurther intelligent shifting strategies. For the purpose of starting theinternal combustion engine in accordance with step b), a higher gearthan the lowest gear is selected above a prespecified minimum speedduring the electric driving mode. In particular, this higher gear islocated in the component transmission which is remote from the electricmotor. The component transmission clutch which is remote from theelectric motor is then shifted to the slip mode, wherein a lower gear isthen engaged in the component transmission which is close to theelectric motor and the component transmission clutch which is remotefrom the electric motor is opened and the component transmission clutchwhich is close to the electric motor is closed, so that there is noslip. Owing to this shifting process, the lower gear is used; itadditionally accelerates the oscillating mass owing to this downshift.

In this context, provision can furthermore advantageously be made, afterstarting of the internal combustion engine, for the torque of saidinternal combustion engine to be passed to the output shaft by at leastpartially closing (slip mode or completely closing) the componenttransmission clutch which is remote from the electric motor. Thecomponent transmission clutch which is close to the electric motor isopened, in particular wherein the electric motor remains engaged untilthe torque of the internal combustion engine increases to the level ofthe torque which is applied to the output shaft by the electric motor.

In the case of electric start-up during the electric driving mode (creepmode), 3rd gear can also be initially selected and a shift can be madeto 2nd gear above a prespecified speed, as a result of which the outputshaft is driven by the electric motor directly by means of 2nd gear. Ina subsequent step, still before closing of the interconnected clutch,the component transmission clutch which is close to the electric motoris opened and the component transmission clutch which is remote from theelectric motor is closed. As a consequence of this, the torque of theelectric motor is introduced into the component transmission which isremote from the electric motor on the output side and into the driveshaft by means of the component transmission which is close to theelectric motor. The torque is therefore returned to a section within thedual-clutch transmission, which section is remote from the motor, in thedirection of the oscillating mass and brought to higher rotation speedsowing to the use of a lower gear. The oscillating mass is accelerated byfinal closing of the component transmission clutch which is remote fromthe electric motor. These steps can also be expedient when the speed ofthe vehicle drops, for example when the vehicle is level or movinguphill again after a start-up process downhill. In this case, therotation speed of the oscillating mass can be increased by means ofdownshifting, even selectively to 1st gear. For the purpose of startingthe internal combustion engine in accordance with step b), the closedcomponent transmission clutch is opened and the interconnected clutch isclosed. It goes without saying that a shift to a higher gear can also beused for reducing the rotation speed.

In general, after starting of the internal combustion engine inaccordance with step b), one of the component transmission clutches canbe closed in order to couple the crankshaft to the output shaft, withoutslip occurring.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of one ormore preferred embodiments when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a first embodiment of the hybrid drivetransmission unit according to the invention, which is suitable forcarrying out the method according to the invention, in the stationarymode.

FIG. 2 shows the hybrid drive transmission unit according to FIG. 1during start-up by the electric motor in a first step of the methodaccording to the invention.

FIG. 3 shows the hybrid drive transmission unit according to FIG. 1 in afollowing step during initial starting of the internal combustionengine.

FIG. 4 shows the hybrid drive transmission unit in a subsequent stepafter starting of the internal combustion engine.

FIG. 5 shows the hybrid drive transmission unit after switch-off of theelectric motor and driving only by means of the internal combustionengine.

FIGS. 6 to 9 show successive steps of the method according to theinvention with the hybrid drive transmission unit according to FIG. 1,wherein the internal combustion engine is engaged in 3rd gear duringstart-up.

FIGS. 10 to 15 show successive steps of the method according to theinvention in accordance with a further embodiment during switch-on ofthe internal combustion engine from creeping driving in 3rd gear.

FIG. 16 shows a further embodiment of the hybrid drive transmission unitaccording to the invention and a first step of the method according tothe invention in accordance with a further embodiment.

FIGS. 17 and 18 show steps of the method according to the invention,said steps following the step according to FIG. 16, in the case ofinitial starting of the internal combustion engine during start-up in2nd gear.

FIGS. 19 to 23 show successive steps of a further embodiment of themethod according to the invention during initial starting of theinternal combustion engine with creeping driving in 2nd gear.

FIGS. 24 to 30 show successive steps of a further variant of the methodaccording to the invention during initial starting of the internalcombustion engine above a prespecified minimum speed.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a drive train of a hybrid vehicle, comprising ahybrid drive transmission unit 10 which is coupled firstly to aninternal combustion engine 12 and secondly to an electric motor 14.

An output shaft 16, which drives wheels 18 in the present case, canselectively be driven by means of the electric motor 14 and/or theinternal combustion engine 12.

The electric motor 14 is permanently coupled into a power-splittransmission 20 (a dual-clutch transmission here). The power-splittransmission 20 has two component transmissions 22, 24, and alsoassociated component transmission clutches 26 and, respectively, 28connected upstream. Torque can be passed to the output shaft 16 by meansof the component transmission 22 or the component transmission 24 orpossibly by means of both component transmissions via the componenttransmission clutches 26, 28.

The component transmission 22 comprises, for example, the even gears 2,4, 6 etc. and also the reverse gear, while the component transmission 24has the odd gears 1, 3, 5 etc. Reference symbol 30 relates to thecoupling tooth systems of the gear stages in the component transmissions22, 24 but also part of the component transmission. Reference symbol 32denotes a controller for the electric motor 14.

The crankshaft 36, which is connected to an interconnected, rapidlyshifting clutch 38 on the output side is first seated on the output sideof the internal combustion engine 12 between the input 34 of thedual-clutch transmission 20 and the internal combustion engine 12. Atorsion damping unit 40, which can be a dual-mass flywheel, a torsiondamper or a rotation speed-adaptive absorber and is provided with one ormore oscillating masses or has coupled thereto, is connected between theclutch 38 and the input 34 of the dual-clutch transmission 20.

The oscillating mass is not illustrated separately; in the illustratedexemplary embodiment, it is integrated in the torsion damping unit 40 ina known manner.

All of the clutches 26, 28, 38 can be electrically switched by means ofa controller which can also be the controller 32.

In the embodiment illustrated in FIG. 1, the electric motor 14 iscoupled into the component transmission 22 in a manner fixed in terms oftorque, specifically downstream of the component transmission clutch 26.For this reason, the component transmission 22 and the componenttransmission clutch 26 are referred to as the component transmissionwhich is close to the electric motor and, respectively, as the componenttransmission clutch which is close to the electric motor, and thecomponent transmission 24 is referred to as the component transmissionwhich is remote from the electric motor and the component transmissionclutch 28 is referred to as the component transmission clutch which isremote from the electric motor.

The interconnected clutch 38 is a rapidly shifting clutch which can beclosed in less than 150 msec, in particular 50 msec.

In the state illustrated in FIG. 1, all of the clutches 26, 28, 38 areopen; the vehicle is stationary.

The vehicle preferably does not have a separate starter for the internalcombustion engine 12, which engine can be started exclusively by meansof the electric motor 14. However, this is not intended to be understoodas restrictive, rather it is also possible for the vehicle to have astarter for the internal combustion engine 12 but to use said starteronly when the vehicle is not in the electric operating mode, but ratheris immediately switched to the combustion mode during starting.

The text which follows will explain, for both of these options, how theinternal combustion engine 12 is driven and started in an abrupt andpulsed manner exclusively by means of the electric motor 14 from thepurely electric driving mode by skilled shifting strategies by way ofthe internal combustion engine being brought to a so-calledself-sustaining rotation speed, even during start-up of the vehicle orin the creep driving mode.

The torque sections identified by arrows specify those torque pathswithin the vehicle and its hybrid drive transmission unit in which atorque is transmitted.

FIG. 2 shows a start-up mode in which the internal combustion engine 12is switched off and the vehicle is operated exclusively by means of theelectric motor 14. Here, the torque runs from the electric motor 14 inthe direction of the component transmission 22 which is close to theelectric motor, via the closed, component transmission clutch 26 whichis close to the electric motor, to the component transmission clutch 28which is remote from the electric motor. The component transmissionclutch 28 is not completely closed here, but rather is in a slip mode,that is to say it continues to transmit a portion of the torque in thedirection of the component transmission 24 which is remote from theelectric motor, from where the output shaft 16 is then finally driven.

Output driving via the component transmission clutch 28 does not takeplace in the component transmission 22 on account of a rotation speedequalization in the synchronization unit.

Since the clutch 38 is open, the crankshaft 36 is not driven. However,the torsion damping unit 40 and its oscillating mass are driven.

Moreover, with respect to the currently selected gear, the correspondinggear is indicated by a circle formed by an interrupted line. In FIG. 2,1 st gear is selected.

Owing to the slip in the component transmission clutch 28, it ispossible to speed up the torsion damping unit 40 to a rotation speedwhich is higher than that rotation speed which is passed to thecomponent transmission 24 downstream of the component transmissionclutch 28. Therefore, the oscillating mass is brought to a higherrotation speed, without the output shaft 16 being accelerated at thesame time.

As soon as a start request is made and a sufficient amount of kineticenergy is available by means of the rapidly rotating oscillating mass inorder to therefore accelerate the internal combustion engine 12 to aself-sustaining rotation speed, the clutch 38 is closed (FIG. 3) and theinternal combustion engine 12 is abruptly carried along and is thereforestarted externally. The clutches 26, 28 can remain in the state in whichthey were in FIG. 2. If jerking is introduced into the power-splittransmission 20 by the abrupt connection, the clutch 28 which is in theslip mode does not transmit this jerking to the output shaft 16.Therefore, the output drive is decoupled from the internal combustionengine via the component transmission clutch 28 in a certain way.

In the next method step (FIG. 4), the internal combustion engine 12 isstarted and itself introduces a torque into the power-split transmission20, as illustrated by arrows. The component transmission clutch 28 isclosed further or completely closed, so that the slip is removed.

The electric motor 14 also introduces a torque into the power-splittransmission 20, so that briefly both the internal combustion engine 12and also the electric motor 14 provide a torque for the output shaft 16.

Then, according to FIG. 5, the component transmission clutch 26 isopened, the electric motor 14 is switched off and driving takes placeonly by means of the internal combustion engine 12. In this case, 2ndgear was already preselected in the component transmission 26, thisagain being symbolized by a circle formed from an interrupted line.However, 2nd gear does not yet transmit torque.

The same hybrid drive transmission unit which is illustrated in FIG. 1and for which the method has already been explained above with FIGS. 2to 5 can also be operated in another situation or generally in adifferent way when, for example, the vehicle starts to drive slightlydownhill or when an electric motor 14 with an extremely high torque isavailable. In this case, the vehicle is not started up in 1st gear butrather in 3rd gear in the component transmission 24.

According to FIG. 6, torque transmission to the output shaft 16 takesplace via the closed component transmission clutch 26 and the componenttransmission clutch 28 which is in the slip mode, and finally by meansof 3rd gear in the component transmission 24. At this time, thecrankshaft 36 is not driven on account of the open clutch 38. However,according to FIG. 2, the oscillating mass of the or in the torquedamping unit 40 is brought to an increased rotation speed.

For the purpose of starting the internal combustion engine, the clutch38 is then suddenly closed according to FIG. 7, in a mannercorresponding to FIG. 3. The output shaft 16 is partially decoupled fromthe internal combustion engine 12 and the crankshaft 36 on account ofthe component transmission clutch 28 which is in the slip mode, so thatno jerking is produced in the output train. The internal combustionengine 12 is abruptly speeded up until it has reached itsself-sustaining rotation speed and started, this being illustrated inFIG. 8 and, apart from the fact that 3rd gear and not 1st gear isselected, corresponding to the state according to FIG. 4.

Then (FIG. 9), as in FIG. 5, the component transmission clutch 26 isopened, the electric motor 14 is switched off and the componenttransmission clutch 28 is closed, so that torque transfer from theelectric motor 14 to the internal combustion engine 12 takes place andonly said internal combustion engine drives the output shaft 16.

This start-up in accordance with the abovementioned method according toFIGS. 2 to 8 takes place only up to a certain prespecified speed.

If the vehicle is above a prespecified minimum speed which cancorrespond to the limit speed just mentioned, the method described belowusing FIGS. 10 to 15 is applied in a creep mode (the vehicle moves veryslowly as before) in order to start the internal combustion engine fromthe electric motor mode. Here, for example according to FIG. 10, 3 rdgear is furthermore selected so that, in the creep mode, only theelectric motor 14 drives the output shaft 16 via the closed componenttransmission clutch 26 and the component transmission clutch 28 which isin the slip mode and the component transmission 24.

It should be stressed in general that, if the vehicle is intended to bedriven only in the electric motor mode and the internal combustionengine 12 is not intended to be switched on, the component transmissionclutch 28 can of course also be completely closed in order to not wasteany energy in the component transmission clutch 28. The componenttransmission clutch 28 is shifted over to the slip mode, this beingexplained above and also being illustrated in FIG. 10 amongst others,only when a corresponding signal for initially starting the internalcombustion engine 12 is output by the controller.

In the creep mode, it may optionally be advantageous to bring theoscillating mass to a higher rotation speed by shifting over the drivepath to the component transmission 22 and using 2nd gear, which issynchronized by slip build up in the component transmission clutch 28,and then to maintain said higher rotation speed, without slip in thecomponent transmission clutches. To this end, according to FIG. 11, thecomponent transmission clutch 28 is opened, so that the torque which isintroduced by the electric motor 14 is firstly supplied by means of thecomponent transmission 22 to the output drive 16 and secondly used viathe closed component transmission clutch 26 to accelerate the torsionmass with clutch 38 open. The clutch 38 according to FIG. 13 may then beabruptly closed when starting of the internal combustion engine isrequired. In this case, a step, explained below, according to FIG. 12 isskipped.

However, in order to be able to shift from 3rd gear to 2nd gear (fromFIG. 10 to FIG. 11), the speed of the vehicle has to have reached atleast a limit speed which allows shifting to 2nd gear. Limit speeds ofthis kind are stored by a controller.

In accordance with the step according to FIG. 11, further speeding up ofthe oscillating mass of the torsion damping unit 40 can optionally beachieved by downshifting to 1st gear. In this case, the componenttransmission clutch 26 is opened, so that no torque can reach thetorsion damping unit 40 via said component transmission clutch. Instead,the torque runs to the output shaft 16 by means of the componenttransmission 22. However, the component transmission clutch 28 is eitherin the slip mode or completely engaged, so that torque is introducedinto the component transmission 24 via the output drive of the componenttransmission 22, where it leads to an increase in the rotation speed ofthe torsion damping unit 40 and the oscillating mass in comparison tothe state according to FIG. 11 on account of the low transmission ratioof 1st gear which is selected.

Therefore, even in the case of a reduction in speed, the kinetic energyin the oscillating mass and the parts which are directly coupled to it,apart from the component transmission clutches 26, 28 for speeding upthe internal combustion engine 12, can be ensured and the componenttransmission clutches 26, 28 can be opened and the clutch 38 can beclosed, as shown in FIG. 13, for initial starting. In this case, theelectric motor 14 cannot introduce any further energy during starting ofthe internal combustion engine, but rather the electric motor 14 nowexclusively drives the output shaft 16. In general, this shiftingbehavior can always be employed given a sufficient rotation speed andthe coupling of the electric motor by means of a selected gear in thecomponent transmission 22.

As soon as the internal combustion engine 12 is started, see FIG. 14,the component transmission clutch 26 is closed, and both the internalcombustion engine 12 and also the electric motor 14 briefly drive theoutput shaft 16.

After the transmission of torque (see FIG. 15), the electric motor 14 isthen switched off. 3rd gear is then already preselected again, while thevehicle is driven in 2nd gear. As an alternative, the componenttransmission clutch 28 can also be closed, the internal combustionengine then drives the output shaft 16 by means of 3rd gear of thecomponent transmission 24; the component transmission clutch 26 is thenopened.

FIG. 16 shows a further embodiment of the hybrid drive transmission unitaccording to the invention which, in principle, is of very similarconstruction to that according to the preceding figures. The onlydifference is that here the electric motor 14 is incorporated fixedly interms of torque in the train of the dual-clutch transmission 20 which isprovided with the lowest gear, that is to say the train with thecomponent transmission 24 and the component transmission clutch 28.Therefore, in this embodiment, the component transmission 24 is thecomponent transmission 24 which is close to the electric motor and thecomponent transmission clutch 28 is the component transmission clutchwhich is close to the electric motor, while the component transmission22 is the component transmission which is remote from the electric motorand the component transmission clutch 26 is the component transmissionclutch which is remote from the electric motor.

According to FIG. 16, the vehicle should start up in 2nd gear by meansof the electric motor 14, so that the component transmission clutch 28is closed and the component transmission clutch 26 is in the slip mode.The clutch 38 is open, and the oscillating mass is brought to a highrotation speed by means of the electric motor 14, without said highrotation speed being passed in the direction of the output shaft 16,this being achieved by the slip mode of the component transmissionclutch 26.

In a manner corresponding to FIG. 2, no torque is passed in thedirection of the output shaft 16 by means of the component transmission24 because no torque is transmitted in the synchronization unit and nogear is engaged.

On request, the clutch 38 is suddenly closed (FIG. 17), so that theinternal combustion engine 12 is brought to the self-sustaining rotationspeed for starting purposes by means of the kinetic energy primarily orexclusively with the aid of the oscillating mass 40 and the rotorinertia of the electric motor 14 here too. However, during this time,the electric motor 14 continues to drive the output shaft 16 by means ofthe component transmission 22. However, as in the previous embodiments,the electric motor 14 can continue to deliver energy to the oscillatingmass during the starting process of the internal combustion engine 12.

FIG. 18 then shows the operation after the transmission of torque to theinternal combustion engine 12 has taken place and the componenttransmission clutch 28 has been opened and the component transmissionclutch 26 has been completely closed. In this case, the electric motor14 is switched off, 2nd gear is engaged and 3rd gear is preselected inorder to shift to 3rd gear during subsequent acceleration.

FIG. 19 shows another driving mode, specifically when the vehicle hasexceeded a prespecified speed and is in creep mode. The prespecifiedspeed is stored here too. In this case, the speed is selected such thata shift to 1st gear can be made owing to the slip in the componenttransmission clutch 26. Here, the electric motor 14 still drives 2ndgear, and therefore the output shaft 16, via the closed componenttransmission clutch 28 and the component transmission clutch 26 which isin the slip mode. The clutch 38 is open and the oscillating mass 40 isaccelerated. Output driving by means of the component transmission 24does not yet take place on account of rotation speed equalization in thesynchronization unit.

By opening the component transmission clutch 26, the torque flow is then(FIG. 20) transferred to the component transmission 24 and the electricmotor 14 drives the output shaft 16 by means of 1st gear. Due to thelower transmission ratio of 1st gear, the oscillating mass 40 rotates ata sufficient rotation speed, without a component transmission clutchhaving to transmit torque in the slip mode.

Therefore, enough kinetic energy is available in the oscillating mass 40in order to start the internal combustion engine by opening thecomponent transmission clutch 28 and then closing the clutch 38, seeFIG. 21, so that exclusively the electric motor 14 supplies kineticenergy to the output shaft 16.

If the engine is started, according to FIG. 22 the componenttransmission clutch 26 is brought at least to the slip mode, so that thetorque of the internal combustion engine is introduced into 2nd gear ofthe component transmission 22 via the component transmission clutch 26and is passed to the output shaft 16, while at the same time theelectric motor 14 also jointly drives the output shaft 16 by means ofthe component transmission 24.

As an alternative, the internal combustion engine 12 can also beconnected to 1st gear by closing the component transmission clutch 28,in which case the component transmission clutch 26 is opened.

FIG. 23 then shows the state with the electric motor switched off anddriving only by means of the internal combustion engine 12.

FIG. 24 shows a starting state when the vehicle is in electric mode butis traveling above a prespecified limit speed.

This limit speed can be the limit speed starting from which the creepspeed is present, or else can lie below said creep speed. However, inpractice, said limit speed can also be higher than the creep speed fordesign reasons. In each case, said speed is selected such that drivingin 1st gear is still possible.

In this situation, the electric motor 14 drives the output shaft 16 bymeans of 1st gear of the component transmission 24 and at the same timethe oscillating mass via the closed component transmission clutch 28.The component transmission clutch 26 is open, and no torque istransmitted by means of the component transmission 22. 2nd gear ispreselected.

However, in this case, the speed of the vehicle is so high that shiftingto 2nd gear is also possible, see FIG. 25, and in the process enoughenergy and rotation speed is available in order to bring the oscillatingmass to the desired minimum rotation speed which is required for drivingthe internal combustion engine at the self-sustaining rotation speed.

In this case, the component transmission clutch 26 is in the slip modeand the component transmission clutch 28 is closed. This allows thetorque flow to be redirected from the component transmission 24 to thecomponent transmission 22 and to reach the output shaft 16 by increasingthe torque in the component transmission clutch 26.

This course, illustrated with reference to FIG. 25, can of course alsobe employed in the hybrid drive transmission unit according to FIG. 1with driving in a low gear and a higher gear would be enough to bringthe oscillating mass to the required rotation speed.

After torque transfer is complete, 1st gear is disengaged according toFIG. 26 and both component transmission clutches 26, 28 are closed. Notorque transmission takes place by means of the component transmission24. The clutch 38 is still open.

The component transmission clutch 26 then enters the slip mode (see FIG.27), while the component transmission clutch 28 remains closed. Here,the oscillating mass can be brought to a higher rotation speed and theoutput shaft 16 can be driven by means of the slip mode in the componenttransmission clutch 26 and furthermore by means of the componenttransmission 22.

The so-called pulse start then takes place according to FIG. 28 byclosing the clutch 38. The component transmission clutch 26 remains inthe slip mode during this start.

FIG. 29 shows the state when the internal combustion engine 12 isstarted.

The component transmission clutch 26 is closed and reduces the slip.Both the internal combustion engine and also the electric motor passtorque by means of the component transmission 22 to the output shaft 16.

Finally, the component transmission clutch 28 can be opened and theelectric motor 14 can be switched off, see FIG. 30.

The electric motor can of course also be connected as a generator forboosting purposes or for recuperation purposes during driving by theinternal combustion engine 12.

In the embodiment according to FIG. 30, the electric motor can beconnected by means of the 1st, 2nd, 3rd, 5th or 7th gear. Correspondingoptions are of course also available for the preceding embodiments. Ingeneral, it should be stressed that both component transmission clutches26, 28 can be opened when enough kinetic energy is available in theoscillating mass, and therefore the power of the electric motor 14 isavailable only for the output drive and is not directed to the internalcombustion engine 12 as well. In this case, the power of the electricmotor 14 can be reduced. As an alternative, when initial starting of theinternal combustion engine is requested, the component transmissionclutch 26 or 28 can also be shifted over to the slip mode, depending onthe embodiment. Therefore, a desired pulse start is likewise possible.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A hybrid drive transmission unit for a vehiclewhich, for drive purposes, has an internal combustion engine and anelectric motor, comprising: a power-split transmission which isinterconnected between the internal combustion engine and an outputshaft, the power-split transmission having component transmissions andassociated component transmission clutches, wherein the electric motoris coupled to a component transmission which is close to the electricmotor in order to be able to drive the output shaft by way of saidcomponent transmission close to the electric motor; a torsion dampingunit interconnected between the internal combustion engine and thepower-split transmission, the damping unit having an oscillating mass;and a clutch which is interconnected between the internal combustionengine and the torsion damping unit.
 2. The hybrid drive transmissionunit according to claim 1, wherein the torsion damping unit is adual-mass flywheel, a torsion damper or a speed-adaptive absorber. 3.The hybrid drive transmission unit according to claim 1, wherein theelectric motor is coupled to that component transmission which containsa 2nd lowest gear.
 4. The hybrid drive transmission unit according toclaim 1, wherein the electric motor is coupled fixedly in terms oftorque to a drive side of the component transmission, between a gear andan associated component transmission clutch.
 5. The hybrid drivetransmission unit according to claim 1, wherein the interconnectedclutch is a rapidly shifting clutch which is closable in fewer than 150msec.
 6. The hybrid drive transmission unit according to claim 1,wherein the interconnected clutch is a rapidly shifting clutch which isclosable in fewer than 50 msec.
 7. A method for operating a vehicle witha hybrid drive including an internal combustion engine, having acrankshaft, and an electric motor, and with a hybrid drive transmissionincluding a power-split transmission interconnected between the internalcombustion engine and an output shaft, a torsion damping unit having anoscillating mass interconnected between the internal combustion engineand the power-split transmission, and an interconnected clutchinterconnected between the internal combustion engine and the torsiondamping unit, wherein the power-split transmission has componenttransmissions and associated component transmission clutches, theelectric motor is coupled to a component transmission which is close tothe electric motor in order to be able to drive the output shaft, acomponent transmission clutch of the component transmission to which theelectric motor is coupled forms a component transmission clutch which isclose to the electric motor, and a component transmission clutch of thecomponent transmission to which the electric motor is not coupled formsa component transmission clutch which is remote from the electric motor,the method comprising the steps of: a) during an electric driving mode,the interconnected clutch is open and the internal combustion engine isswitched off; and b) starting the internal combustion engine by closingthe interconnected clutch and by transmitting kinetic energy of theoscillating mass which is driven during the electric driving mode to thecrankshaft in order to bring the internal combustion engine to aself-sustaining rotation speed.
 8. The method according to claim 7,wherein before closing the interconnected clutch for starting purposesin accordance with step b) and when a prespecified minimum rotationspeed of the oscillating mass is reached, the component transmissionclutches are open or held in a slip mode, wherein the electric motorfurther drives the vehicle until the internal combustion engine appliesa prespecified torque.
 9. The method according to claim 8, wherein forstarting in accordance with step b) at a vehicle speed below aprespecified speed, before closing the interconnected clutch and/orafter closing the interconnected clutch, the output-side componenttransmission clutch from amongst the two component transmission clutcheswill be or is shifted to the slip mode.
 10. The method according toclaim 9, wherein the output-side component transmission clutch, in theslip mode, is adjusted and the electric motor is brought to a rotationspeed such that a required torque is applied to the output shaft by theelectric motor and/or the oscillating mass is accelerated to aprespecified minimum rotation speed.
 11. The method according to claim10, wherein the interconnected clutch is opened immediately before abeginning of the slip mode and/or wherein the slip mode is maintainedduring starting of the internal combustion engine in step b).
 12. Themethod according to claim 7, wherein for starting in accordance withstep b) at a vehicle speed below a prespecified speed and/or duringstarting in accordance with step b) during start-up of the vehicle, thecomponent transmission clutch which is close to the electric motor isclosed and the component transmission clutch which is remote from theelectric motor is brought to a slip mode, the torque of the electricmotor is transmitted to the output shaft via the two componenttransmission clutches and by way of the component transmission which isremote from the electric motor.
 13. The method according to claim 12,wherein after closing the interconnected clutch, the componenttransmission clutch which is close to the electric motor remains closedand the component transmission clutch which is remote from the electricmotor remains in the slip mode, until the internal combustion enginestarts.
 14. The method according to claim 13, wherein after starting theinternal combustion engine in accordance with step b), the componenttransmission clutch which is remote from the electric motor is closed,and, when the torque which is introduced into the power-splittransmission by the electric motor is reached or exceeded by the torquewhich is introduced into the power-split transmission by the internalcombustion engine, the component transmission clutch which is close tothe electric motor is opened, so that torque passes to the output shaftexclusively by way of the internal combustion engine.
 15. The methodaccording to claim 7, wherein for the purpose of starting the internalcombustion engine in accordance with step b), a higher gear than thelowest gear is selected above a prespecified minimum speed during theelectric driving mode, wherein said higher gear is located in thecomponent transmission which is remote from the electric motor, and thecomponent transmission clutch which is remote from the electric motor isshifted to the slip mode, wherein a lower gear is then engaged in thecomponent transmission which is close to the electric motor and thecomponent transmission clutch which is remote from the electric motor isopened, so that the oscillating mass is accelerated on account of thelower gear.
 16. The method according to claim 15, wherein after startingthe internal combustion engine, the torque of said internal combustionengine is passed to the output shaft by at least partially closing thecomponent transmission clutch which is remote from the electric motorand the component transmission clutch which is close to the electricmotor is opened, wherein the electric motor remains engaged until thetorque of the internal combustion engine increases to the level of thetorque of the electric motor which is applied to the output shaft. 17.The method according to claim 16, wherein for the purpose of startingthe internal combustion engine in accordance with step b), 3rd gear isinitially selected above a prespecified minimum speed during theelectric driving mode, then a downshift to 2nd gear occurs and theoutput shaft is driven by the electric motor above 2nd gear and, in afollowing step, still before closing the interconnected clutch, thecomponent transmission clutch which is close to the electric motor isopened and the component transmission clutch which is remote from theelectric motor is closed, so that the torque of the electric motor isintroduced into the component transmission which is remote from theelectric motor by way of the component transmission which is close tothe electric motor and the output shaft, and the oscillating mass isaccelerated by closing the component transmission clutch which is remotefrom the electric motor.
 18. The method according to claim 7, whereinafter starting the internal combustion engine in accordance with stepb), one of the component transmission clutches is closed in order tocouple the crankshaft to the output shaft.